/* ===== ROOT VARIABLES ===== */
:root {
    --bg-body: #ffffff;
    --surface: #ffffff;
    --surface-soft: #f8f9fa;
    --text-primary: #1e293b;
    --text-secondary: #475569;
    --border: #e2e8f0;
    --accent: #2563eb;
    --header-height: 70px;
    --transition: all 0.2s ease;
}
[data-theme="dark"] {
    --bg-body: #0f172a;
    --surface: #1e293b;
    --surface-soft: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --border: #334155;
    --accent: #3b82f6;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    background: var(--bg-body);
    color: var(--text-primary);
    font-family: 'Inter', sans-serif;
    line-height: 1.5;
    transition: background 0.2s, color 0.2s;
}
.skip-link {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--accent);
    color: white;
    padding: 8px;
    text-decoration: none;
    z-index: 200;
}
.skip-link:focus { top: 0; }

/* ===== HEADER ===== */
.site-header {
    background: var(--surface);
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 100;
    height: var(--header-height);
    display: flex;
    align-items: center;
    backdrop-filter: none; /* ডার্ক মোডে কোনো সমস্যা নেই */
}
[data-theme="dark"] .site-header {
    background: var(--surface);
    border-bottom-color: var(--border);
}
.header-container {
    max-width: 1280px;
    width: 100%;
    margin: 0 auto;
    padding: 0 1.5rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1.5rem;
}
.logo {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    font-weight: 600;
    font-size: 1.25rem;
    color: var(--text-primary);
}
.desktop-nav ul {
    display: flex;
    gap: 2rem;
    list-style: none;
}
.desktop-nav .nav-link {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    transition: var(--transition);
}
.desktop-nav .nav-link.active,
.desktop-nav .nav-link:hover { color: var(--accent); }
.header-actions {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

/* Theme Toggle */
.theme-toggle {
    background: none;
    border: none;
    cursor: pointer;
    padding: 8px;
    border-radius: 50%;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    color: var(--text-primary);
}
.theme-toggle .moon-icon { display: none; }
[data-theme="dark"] .theme-toggle .sun-icon { display: none; }
[data-theme="dark"] .theme-toggle .moon-icon { display: block; }

/* Mobile Menu Button (Hamburger) */
.mobile-menu-btn {
    background: none;
    border: none;
    cursor: pointer;
    width: 40px;
    height: 40px;
    display: none;
    flex-direction: column;
    justify-content: center;
    gap: 6px;
    padding: 0;
}
.hamburger-line {
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    transition: 0.2s;
    display: block;
    margin: 0 auto;
}
.mobile-menu-btn[aria-expanded="true"] .hamburger-line:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}
.mobile-menu-btn[aria-expanded="true"] .hamburger-line:nth-child(2) { opacity: 0; }
.mobile-menu-btn[aria-expanded="true"] .hamburger-line:nth-child(3) {
    transform: rotate(-45deg) translate(6px, -6px);
}

/* ===== MOBILE MENU (LEFT SLIDE, FULL HEIGHT BELOW HEADER) ===== */
.mobile-nav-panel {
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    bottom: 0;
    visibility: hidden;
    z-index: 90;
}
.mobile-nav-panel.active { visibility: visible; }
.mobile-nav-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    opacity: 0;
    transition: opacity 0.3s;
}
.mobile-nav-panel.active .mobile-nav-overlay { opacity: 1; }
.mobile-nav-container {
    position: absolute;
    top: 0;
    left: 0;
    width: 85%;
    max-width: 320px;
    height: 100%;
    background: var(--surface);
    transform: translateX(-100%);
    transition: transform 0.3s cubic-bezier(0.2, 0.9, 0.4, 1.1);
    padding: 1.5rem;
    overflow-y: auto;
    /*border-radius: 0 20px 20px 0;*/
    box-shadow: 2px 0 12px rgba(0,0,0,0.1);
}
.mobile-nav-panel.active .mobile-nav-container { transform: translateX(0); }
.mobile-nav-list {
    list-style: none;
    padding: 0;
}
.mobile-nav-list li { margin-bottom: 1.5rem; }
.mobile-nav-link {
    font-size: 1.3rem;
    font-weight: 500;
    color: var(--text-primary);
    text-decoration: none;
    display: block;
    padding: 0.5rem 0;
    border-bottom: 1px solid var(--border);
}
.mobile-nav-link.active { color: var(--accent); }

/* Footer */
.site-footer {
    background: var(--surface);
    border-top: 1px solid var(--border);
    padding: 1.5rem;
    text-align: center;
    color: var(--text-secondary);
}

/* Responsive */
@media (max-width: 768px) {
    .desktop-nav { display: none; }
    .mobile-menu-btn { display: flex; }
}
@media (min-width: 769px) {
    .mobile-nav-panel { display: none; }
}